Worn brush indicator

Abstract

A worn brush indicator for machinery, e.g., a motor generator, wherein a carbon brush is in engagement with a moving contactor, e.g., a commutator or slip ring. The brush is made with an elongated cavity, and an insulated conductor is placed in the cavity. When the brush is worn to a point where the cavity is exposed and the insulating is worn away, the conductive member, having a carbon tip, engages the commutator, and an alarm circuit connected between the conductive member and the brush proper signals a worn brush condition.

I claim: 
     
       1. A worn brush indicator for an electrical machine having a rotating commutator, at least one brush holder, and a carbon brush member in said brush holder, each brush member having a conductive body and face end for effecting a sliding and conductive contact with said commutator comprising: a cavity in said brush member extending through said brush member from an end region opposite to said face end of said brush member and toward said face end for a selected distance;   an insulating sleeve in said cavity;   a conductive member extending through said insulating sleeve to a point which is a selected distance from the face of said brush and having an essentially non-abrasive terminating surface; and   signal detection means electrically connected between the body of a said brush member and a said conductive member, and including means for signalling a worn brush member when an electrical circuit is completed between a said conductive member, through said commutator, and to the body of a said brush member;   whereby, when said brush member is worn to a selected degree, said conductive member electrically engages said commutator and thereby signals a worn brush condition.   
     
     
       2. An indicator as set forth in claim 1 wherein said machine includes first and second said brush holders, and first and second brush members in engagement with said commutator, and said signal detection means is in circuit between the conductive member of said first brush member and the body of said second brush member and between the conductive member of said second brush member and the body of said first brush member for signalling when one of said brush members is worn by a selected amount.